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White, earthy powder used for optical glass, 6 letters
Element in vacuum tube filaments, 7 letters
Metal that's an effective radiation shield, 7 letters
A soft silvery-white tetravalent radioactive metallic element, 7 letters
Isotope 232 is used as a power source in nuclear reactors, 7 letters
Occurs in thorite and in monazite sands, 7 letters
A radioactive mineral consisting of thorium silicate, 7 letters
It is a source of thorium that is found in coarse granite, 7 letters